Process of and apparatus for electrolytic production of caustic alkali.



H. H. DOW. PROCESS OF AND APPARATUS FOR ELECTROLYTIC PRODUCTION OF CAUST IC ALKALI. APPLICATION FILED AUG-12,1915.

1 ,284,6 1 8. Patented Nov. 12, 1918;

2 SHEETS-SHEET l- JII 1 H. H. DOW.

PROCESS OF AND APPARATUS FOR ELECTROLYTIC PRODUCTION OF CAUSTIC ALKALI.

APPLICATION FILED AUG-12,1915.

Patented Nov. 12, 1918.

2 SHEETS-SHEET 2- Unreal) STATES PAT NTor IcE.

I-IERBEI'iTT-IIDOW, F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COM- PANY, 0F MIDLAND, MICHIGAN, A CORPORATION OEMICHIGAN.

".To all whom z'tmay concern: I

' Be it known that I, HERBERT H. Dow, a

. citizen of. the United States, residing at .Midland, in the eountyof Midland and State of Michigan, have invented a certain new and useful Improvement in Processes of and Apparatus for Electrolytic Pr0duc- 'tion of Caustic Alkali, of which the followprovision of a method and apparatus whereby the power consumption may be rendered more etficient, whereby the liquid 'efiluent may be obtained in a. more pure state and i with fewer by-products and impuritles than heretofore, and whereby the cell destruction, particularly the anode erosion, may be decreased. While the improvements hereinafter described may be of value in other relations, they have been especially perfected for the purpose of electrolyzmg alkali chlorids for the production of ehlorin and caustic, and the following description will be based upon the electrolyzation of common salt for the production of chlorin and .caustic soda, although it will be understood that the same is applicable wholly without change for the electrolysis of any halid salt whose base yields a hydroxid soluble in water, and may be available for other uses in addition, wherefore I do not limit myself except as particularly stated in the claims hereto amiexed'.

The principle of my invention consists in this, that the electrolysis isconducted in a series ofcells, the catholyte being also ad- ,vancedwfrom cell to cell so as to receive an increment in its causticity in each succeeding'cell. The advantage of this method is I that the average causticity of the catholyte f tion' performed in each cell; for example,

is maintained at a lower point than would be the case if the separate cells were operated individually and the complete reduc in case all the cells were fed with catholyte liquor in parallel. According to my improved process the causticity of the catholyte liquor varies progressively from the first to the last cell of the series, the average causticity being materially less than Specification of Letters Patent.

PROCESEQGF AND APPARATUS FOR ELECTROLYTIC PRODUCTION OF CAUSTIC ALKALIQ Patented Nov. 12, 1918.

Application filed August 12, 1915. 1 Serial No. 45,097.

that of the final eliiue'nt. In other systems of workingwith whichI am familiar the final causticity is obtained in everyeell so that the average causticity and the final causticity are'substantially or exactly the same thing. It is well settled, both theoretically and practically, that in the electrolysis of a halid solution for halid and caustic, the presence of strong caustic liquor in the cathodecompartment of the cell serves both to diminish the current efficiency and to impair the purityof the caustic product. The.

theoretical explanations of this condition are somewhat abstruse and possibly not definitely settled, but the existenceof the fact,

is well established' It. is'known that at low causticities and small concentrations the current efficiency is comparatively high and the contamination of the efiluent with secondary reduction products is very small, but practical considerations do not permit the full utilizationof these conditions since the cost of evaporating such a large quantity of liquid, and the extremely large plant required to handle a commercial business necessitates the employment of a higher concentration.

As one means for diminishing such secondary reactions, it has heretofore been proposed to provide each cell with a porous diaphragm located between the anode "and cathode, and to maintain a higher static pressure of the anolyte than of the catholyte, thus mechanically opposing the difl'usien or migration of ions from the cathode to the anode, and increasing the current efficiency and the purity of product. The porosity of the diaphragm permits a slow percolation of the electrolyte from the an ode compartment to thecatliode compartunent, and in some systems'this percolation 1S depended upon for the maintenance of catholyte during electrolysis.

. j I have discovered that in case the catho-' lyte'be withdrawnfrom each cell after having been electrolized a certain amount and be added to thecathode chamber of a'succeedmg celhand be there eleetrolyzed a certaln amount and afterward transferred to a third cell, and so on, the efiiciency of the cell system may be considerably improved, and

the contamination of the final product and the average-destruction of the anodes much Thus the average iuimical ctl'ect oi' these operations is reduced over what would he the case it all the cells were run. in parallel as heretofore, since with the parallel ar rangement there is present. a maxinuun ditt'erence ol liquid composition in allot the cells; also with this arrangement am enabled to employ a less pervious diaphragm, and one which by its nuchanical construction is better constituted to prevent the dittusion hereto't ore mentioned. in oreer to secure the requisite electrolytic ctl'cct it'is probably necessary to employ a diaphragm ot' such porosity that some percolation will take place. although the feeding: of the catholyte chamber by pe rotation as has heen common in previous methods has necessitated the employment ol a more porous dia-iphragm than is required for the electrical purposes oi the apparatus, liccordintr to my invention the major part of the -atholyte is derived from a. precediin cell. and only a minor portion ot the same by percolation through the dia plll'ttflllt. 'lhe working of my invention does not depend to any degree upon the derivation of the catholyte liquor from the anode side ot the eellsnt any point ot' the cell series; even though, as a result of diaphragm porosity. a certain amount of anolyteslumld pass to the eatholytc at each cell. this is entircly apart t'rom the merits of the present invention. it is the essence ot this invention that the catholyte be derived mainly, and lll'ttt'l'tlld) entirely, trom the cathode compartment ol a preceding cell. to the end that the composition diti'crence hetween the. anolyte and eatholyte, and the catholyte causticity may vary progressively lrom one end ol' the series to the other, which result would he obtained in its greatest ethcieney in case the diaphragm ptu'colation could be wholly eliminated.

It is wholly imnmterial to this invention how the nodechambers ol' the'various cells are maintained. "hey may he ted separately or in parallel; they may he ted in series. one from the other: it t ed in series, the direction oi flow may he either parallel or opposite to that of the catholyte tlow; the spent liquor from the anode compartments may he rcsaturated with halid and.

returned as anolyte feed, or it may be' employed tor the catholyte liquor. As a matter of convenience it prefer to return through the cathode chambers the anode liquor which has previously passed through the anode chambers, owing to'the fact that in composition, comwntration, temperature, conductivity, and the like respects it is fully suit.- able and because it present in the right quantities and at a convenient: place, but this is wholly a matter of choice.

flu the drawii'igs accompanying and forming; a part" oil? this application-I have illustrated certain apparatus whereby the 1neth ods and objects of this invention may be realized, although it will he understood that these drawings are merely. diagramn'iatic, and that they are not intended to be exlrustijve of all the arrangements, c0nnections, or systems whereby the principle of my invention may he utilized. In said drawings each tigrure illustrates diagrannnatically an arrangement or" cells by Which the principle of my present invention may he uti- 'tizcd. l ip'ures 'l and 3 illustrate an arrangement in which the flow of the anolyte and catholyte are in opposite directions; hugs. '3 and an a rrangrement in which the anotyte and catholye How in the same di rection; and Fig. 5 an arrangementin which the anolyte and catholyte are entirely dis tinct from each other.

l lach figure. of the drawings shows three cells, indicated by l, H and 1H, although it will he understood that the number could he continued to any length desired, and will ordinarily in practice be extended to much greater length so that when the cells are connected in series electrically, a convenient commercial volt ige may be utilized while atl'ording each cell the E. M. F. necessary to its most etlicient pertormancc. However, so far as the present invention is concerned, it is wholly immaterial whether the electrodes be connected inseries or in parallel or even whether they are ted from the same current source or ditl'erent sources.

in each of the views of the drawing the cell container is indicated at E, the anode at A, the cathode at C and the diaphragm at D. in the apparatus illustrated in Figs. 1 to st inclusive the raw brine is admitted by the conduit (1. to the firstanode chamber, aind thence by conduit (5 etc., to the succeeding anode chambers, being then trans ferred by a. conduit (4 to a cathode chamber, whence it; is transferred by conduits 0 0' etca to-the remaining cathode chambers of the series, beingultimately discharged at the outlet The liquid upon the anode side of each cell is shown at a slightly higher level than that on the cathode side of that cell so as to inducethc percolation through the diaphra ni heretofore mentioned. In Fig. t

catholyte, so that liquid from the last anode I have illustrated the successive cells as placed at different levels so as to provide the gradient necessary to the free flow of liquid from chamber to chamber. In this instance it will be noted that the total difierence the height of the cells is less than the difference in height between the anolyte and chamber can flow directly into the first cathode chamber. In case the series of cells were longer or the diiference in height greater, a suitable elevating device could be introduced in the pipe a such as a pump or worm.

In Fig. 5 I have illustrated an arran ement wherein the anode chambers are ed independently of each other as by the inlets a, a, and a, the efliuent therefrom being conveyed away by the outlets m x 00 to a conduit y and discarded or otherwise utilized, the various cathode chambers being fed independently from a source 8 and the catholyte passing from cell to cell by conduits 0 0, etc, as before, and finally appearing at the outlet 0 fed to both" anode and cathode cells in this arrangement, the operation is exactly the same as that above described, with the possible advantage that with the arrangement in Fig. 5 the anode cells all contain liquid of the same composition and conductivity, while in Figs. 1 to 4. inclusive the anolyte is slowly being drained of its halid content. In order to prevent the undue impoverishment of the anolyte with the arrangement shown in Figs. 1 to 4 inclusive, it is necessary in the case of a long'series of cells to introduce raw brine at intervals into the anolyte stream. However, the expedient of reducing the halid content of the anolyte before introducing this liquid into the cathode chambers is sometimes advantageous, both as reducing the total concentration of the catholyte and diminishing the amount of halid to be removed from the solution.

I have already pointed out that my improvements are independent of the derivation of catholyte by percolation ot' anolyte through the celldiaphragm, although it is necessary to make provision for some such percolation since the'same may be expected to some degree in practice. It can be proved,

both by theoretical deduction ahd practical I demonstration, that by the employment of a series electrolysis such herein described and claimed, the difference in.electrolyte composition between difi'erent cells is greater and the. average concentration and causticity In case the same liquid be.

be derived from two sources, namely by percolation through the diaphragm of that same cell, and by accretion from the cathode chamber of the preceding cell. .'.From one aspect it may be stated that my est practical .value.

It will be understood that I have shown only a few out of many forms of apparatus with which my improved process can be carried out, and described only apart of the benefits to be derived therefrom, and considered only a part of the uses to which such process and apparatus can be put.

Having thus described my invention What I claim is:

1. Apparatus for producing an alkali hydrate and chlorin from an alkali chlorid by electrolysis, comprising a series of electrolytic cells each having a diaphragm of limited permeability to liquid whereby the cell is divided into an anode compartment and a cathode compartment, each compartment of each cell having an inlet and an outlet,

the first cathode inlet the effluent from the anode outlets. 2. Apparatus for producing an alkali hydrate and chlorin from an alkali chlorid by electrolysis, comprising a series of electrolytic cells each havin a diaphragm of limited permeability to hquid whereby the cell is divided into an anode compartment and a cathode compartment, each compartment of each cell having an inlet and an outlet, the outlet of each catholyte compartment communicating with the inlet of a succeeding catholyte compartment, until the last of the series is reached, the outlet of each anode compartment communicating with the inlet of a succeeding anode compartment until the last is reached, the outlet from the last anode compz'u'tment comn'iunicating With the inlet of the first cathode compartment, means for n'lain'tainmg the level of the anolyte in each cell above that of the catholyte of that cell, and means for delivering halid solution to 'the first anode compartment.

In a method of electrolyzing an alkali halid solution for caustic and halid, the step which consists in passing the solution first through the anode compartments of a plurality of diaphragm cells and then passing the same solution successively through the cathode compartments of said cells.

4. The process oi? electrolyzing an alkali halid solution for halid and caustic alkali which consists in adding to the anode chambcr eta diaphragm cell greater quantity oi solution than said diaphragm can transmit by percolation, drawing ell the excess of such liquid and passing it into the cathode chan'iber of the same or a similar cell by a separate passage, and thereafter passing said liquid through the cathode chambers of a plurality of similar cells until the desired causticity is attained.

The process of electrolyzing alkali halid solution :t'or halid and caustic alkali which consists in adding to the anode chambers of a plurality of separate electrolytic cells ot the diaphragm type, a quantity of solution greater than the diaphragn'is can transmit by percolation, drawing otl the excess of such solution after treatment in such anode chambers and. passing it successiyely through all the'cathode chambers out the series.

(3. The process of electrolyzing alkali halid solutions for halid and caustic alkali which consists in adding to the anode chambers of a plurality of separate electrolytic cells ot the diaphragm type, a quantity of solution greater than the diaph'ragms can transmit by percolation, drawing oil the eX- cess of such solution after treatment in such anode chambers and passing it successively through all the cathode chambers of the series, and meanwhile maintaining in each. said cathode chamber a pressure of liquid less than that in the corresponding anode chamber.

7. Apparatus for electrolyzing alkali halid solution to produce halid and caustic alkali, comprising two electrolytic cells of the porous diaphragn'i type, the anode compartments being connected in series so as to permit the flow'ot' liquid from one to the other, the cathode chambers being also con nected in series so as to permit the How of liquid from one to the other, and the last anode chamber being connected to the first cathode chamber so that the spent a'nolyte may pass through the cathodechambers.

8. A series of electrolytic cellsot the porous liaphragm type, the anolyte being fed into the anode compartment through a suitable rmssageway and withdrawn from the anode compartment through the porous diaphragm and another suitable passage 'ay, the catholyte being ted into each compartment through a suitable passage and also through the pores of the diaphragm and withdrawn through a passage connected with the cathode compartment or another cell of the series, the effluentfroin the last anode compartment of the series lowing to a cathode compartment and from thence to each cathode compartment in succession.

9. The method of electrolyzing an alkali halid solution for caustic andhalid which consists in first passing the halid solution successively through the anode compartments of a plurality of independent electrolytic cells of the diaphragm type, and second returning the same liquid successively through the cathode compartments of the same cells in reverse order.

In testimony whereof, l hereunto aliix my signature in the presence of two witnesses.

Illfiltlllillil. ll-l'. DOV. l i itnesses James T. Panonn, A. "W. thorn. 

